Traditionally, stroke in children and young adults has been linked to diverse etiologies such as trauma, congenital heart disease, and autoimmune and hematologic diseases, while atherosclerotic risk factors have been considered unimportant. However, autopsy and carotid ultrasound studies suggest that atherosclerosis begins in childhood, and recent epidemiological studies suggest that atherosclerotic risk factors are increasingly prevalent among adolescents and young adults with stroke. Black race confers a similariy increased stroke risk in both children and adults, and the excess risk in black children does not appear to be fully explained by sickle cell disease. We hypothesize that stroke rates in the young have increased over the last 2 decades, and that race and atherosclerotic risk factors play a role in this increase. The specific aims are: Aim 1: To develop a highly sensitive and specific algorithm for using electronic data to identify ischemic stroke and atherosclerotic risk factors (hypertension, hyperiipidemia, diabetes mellitus, obesity, smoking) in a cohort of children and adults in KPNC, and to validate this algorithm in a separate cohort within KPNC. Aim 2: In a large population-based cohort of children and young adults (<age 50) within KPNC over a 15- year time period: a. To determine the overall trend in the incidence rate of ischemic stroke, and to evaluate the trend in stroke incidence rates among subgroups of race and gender. b. Among a sub-cohort of members hospitalized for stroke, to determine the overall trends in the prevalence of atherosclerotic risk factors, and to evaluate the trends in prevalence of these risk factors among subgroups of race and gender. Aim 3: In a case-control study nested within the cohort of children and young adults in KNPC, to evaluate the role of socioeconomic status, atherosclerotic risk factors, trauma, sickle cell disease, and other stroke risk factors, in the ethnic disparities of stroke incidence.